Flirting with the Dark Side

FLIRTING WITH THE DARK SIDE

Scripting and AI

Damián Isla, Moonshot Games

Scripting vs. Scripting

Distinguish between scripting as technology and scripting as filthy hackery.

Scripting as Filthy Hackery

“Lazy devs faking it in script instead of doing it for real in code.”

Obviously absurd.

Code doesn’t make it more real. Script is code. It’s all fakery if you go down far enough.

Faking it

Robust vs. brittle systems Orthogonal to questions of implementation language

Robust is always better

A Matter of Economics we don’t have time to do everything well it works most of the time

The World is Lies

... so what we should be asking ourselves is not “how do we avoid faking it” but “what’s the best way to fake it?”

The Most Important AI Technology Ever

if <X> then <Y> else <Z>

But this sucks

if (ai.health < health_cover_threshold){

<Y> }else {

<Z>}

Scripting as Architecture

LUA Compiled to bytecode Hot swapping Highly embeddable Highly customizable Dynamic typing

Months of dev time

saved

Kill me now

Pros and Cons

We like Iteration times Expressivity Designer-accessibility

We don’t like Performance Designer-accessibility

El Compromiso

Systems that are performance-sensitive are generally NOT the systems where designer-expressivity is important.

And vice versa.

Our Strategy

Script as a pillar of the the Engine

Component object model Components can be

implemented in C++ Lua

Script is also the special sauce

Script is the glue

The [Production] Goal

Lua can be used to create first-class systems from the ground up.

3 parts: component scripts system scripts data

Components and Script

A B

C

D

Components and Script

A B

Components and Script

APath

This is where the fun lives

BAnimation

Component Soup

A*Perceptio

n/Ray-casting Target

selection

Behavior

Physics

Animation

playback

Animation control

Squad behavi

orRandom

Script

Component Soup

A*Perceptio

n/Ray-casting Target

selection

Behavior

Physics

Animation

playback

Animation control

Squad behavi

orRandom

Script

Emit balloons from ears whenever player hits the

elephant with the frying pan

Component Soup

A*Perceptio

n/Ray-casting Target

selection

Behavior

Physics

Animation

playback

Animation control

Squad behavi

orRandom

Script

Component Soup

A*Perceptio

n/Ray-casting Target

selection

Behavior

Physics

Animation

playback

Animation control

Squad behavi

orRandom

Script

Component Soup

A*Perceptio

n/Ray-casting Target

selection

Behavior

Physics

Animation

playback

Animation script

Squad behavi

orRandom

Script

Locomotion control

Component Soup

emit_balloons

initialize()attach()update()detach()

System Soup

System script

System Soup

Boids

System Soup

Data Need to be able to:

save out the state of the scripts drive the system with data define the structure for both

Lua can define structures define structures for engine-allocated data blocks engine controls the lifetime of these blocks

Lua reads and writes to the blocks is NEVER allowed to allocate it’s own dynamic memory we lock the global scope after creation

System Soup

Parameters State

Parameters State

System script

Script-based Systems

What it gets us

A fluid design environment avoid the “data-driven” code trap

A place to put our hacks (Embrace the hackery)

Continuity between prototyping and production

Initial Framework (Engineer)

Implementation (Design)

Final implementation (Engineer)

Final buy-off (Design)

Engineer makes it

work

Design makes it work well

Engineer makes it fast

Design makes sure it still works well

Not so fast...

Doesn’t mean you don’t need to

Provide perf tools Think systemically about script Think seriously about interfaces between components Design all pieces as an architecture Help designers write good systems, not just good code

But does mean that the architecture can evolve more fluidly and in a more design-driven way.

Concepts that don’t Exist (In code) Health / Death / Damage Weapons / Items / Equipment / Powers AI Behavior HUD / UI / Menus Missions / Levels / Objectives

One more distinction

C++ high performance low (designer) expressivity game-agnostic

Script low performance high (designer) expressivity game-specific

The technology you keep

around for next timeThe stuff that makes this

game unique and awesome

Thanks!